1. Field of the Invention
This invention relates generally to an apparatus and method for providing stochastic independent neural stimulation, and in particular, a neural stimulation system and method for identifying candidates for intervention and treatment of tinnitus by initiating pseudospontaneous activity in the auditory nerve.
2. Background of the Related Art
Fundamental differences currently exist between electrical stimulation and acoustic stimulation of the auditory nerve. Electrical stimulation of the auditory nerve, for example, via a cochlear implant, generally results in more cross-fiber synchrony, less within fiber jitter, and less dynamic range, as compared with acoustic stimulation which occurs in individuals having normal hearing.
FIG. 1 shows the magnitude of a related art pattern of electrically-evoked compound action potentials (EAPs) from an auditory nerve of a human subject with an electrical stimulus of 1 kHz (1016 pulses/s). The EAP magnitudes are normalized to the magnitude of the first EAP in the record. FIG. 1 shows the typical alternating pattern previously described in the art. This pattern arises because of the refractory period of the nerve and can degrade the neural representation of the stimulus envelope. With a first stimulus 102 a large response occurs, likely because of synchronous activation of a large number of fibers. These fibers are subsequently refractory driving a second pulse 104, and accordingly a small response is generated. By the time of a third pulse 106, an increased pool of fibers becomes available (non-refractory) and the corresponding response increases. The alternating synchronized response pattern can be caused by a lack or decrease of spontaneous activity in the auditory nerve and can continue indefinitely.
Loss of spontaneous activity in the auditory nerve is one proposed mechanism for tinnitus. Proposed biological mechanisms for the loss of spontaneous activity in the auditory nerve include loss of hair cells in the cochlea. In addition, the loss of hair cells over time is a proposed mechanism for the loss of auditory neurons likely caused by related activities at synapses connecting the hair cells to the auditory neurons in the cochlea.
Tinnitus is a disorder where a patient experiences a sound sensation within the head (xe2x80x9ca ringing in the earsxe2x80x9d) in the absence of an external stimulus. This uncontrollable ringing can be extremely uncomfortable and often results in severe disability. Restoration of spontaneous activity may potentially improve tinnitus suppression. Tinnitus is a very common disorder affecting an estimated 15% of the U.S. population according to the National Institutes for Health, 1989 National Strategic Research Plan. Hence, approximately 9 million Americans have clinically significant tinnitus with 2 million of those being severely disabled by the disorder.
Methods and apparatus that generate stochastically independent or xe2x80x9cpseudospontaneousxe2x80x9d neural activity in the auditory nerve have been modeled and tested with discernable improvements in auditory capabilities including reductions in tinnitus. See U.S. patent application Ser. No. 09/023,279 filed on Feb. 13, 1998, entitled xe2x80x9cSpeech Processing System and Method Using Pseudospontaneous Stimulation,xe2x80x9d which is hereby incorporated by reference. However, biological and somatosensory responses to gradual or rapid reversals of the loss of spontaneous activity in the auditory nerve, for example, were heretofore unknown. Preferably, pseudospontaneous neural activity would be introduced without perception to a patient. For example, in an auditory nerve the desired treatments of tinnitus associated with sensorineural hearing loss would suppress the tinnitus without producing any additional sensations and auditory percepts.
At this time the only clinically effective treatment that actually decreases the perception of tinnitus is acoustic masking. While this is helpful for some patients, for others it simply replaces one undesirable sound with another. An ideal therapy for tinnitus would create the perception of silence or at least decrease the loudness of tinnitus without introducing any new sounds. Further, there is no current method to identify successful treatment regimes based on tinnitus characteristics.
An object of the present invention is to provide an apparatus and method of neural stimulation that substantially reduces or obviates at least one of the problems caused by disadvantages of the related art.
Another object of the present invention is to provide an apparatus and method that imperceptibly generates stochastically independent or xe2x80x9cpseudospontaneousxe2x80x9d neural activity.
Yet another object of the present invention is to provide an apparatus and method that imperceptibly generates statistically independent or xe2x80x9cpseudospontaneousxe2x80x9d activity in an auditory nerve to suppress tinnitus.
Still yet another object of the present invention is to provide an inner ear or middle ear auditory prosthesis that suppresses tinnitus without producing additional sensations.
A further object of the present invention is to provide an apparatus and method that determines candidates for treatment of tinnitus using neural prosthetics.
A further object of the present invention is to provide an apparatus and method that determines candidates for treatment of tinnitus using neural prosthetics to generate pseudospontaneous activity in an auditory nerve.
A still further object of the present invention is to provide an apparatus and method that provides a diagnostic for significant reduction of tinnitus perceptions through treatment.
A still further object of the present invention is to provide an apparatus and method that tests whether a patient""s tinnitus can be at least partially reduced.
A still further object of the present invention is to provide an apparatus and method that selects candidates for transtympanic electrical suppression of tinnitus.
A still further object of the present invention is to provide an apparatus and method that determines residual effects of applying signals capable of generating pseudospontaneous activity in a nerve.
To achieve at least the above objects in a whole or in parts, there is provided a method of diagnosing whether a human is a candidate for tinnitus reduction using a neural prosthetic, including applying an electrical signal capable of generating pseudospontaneous activity in an auditory nerve of at least one human to a plurality of candidates, identifying a prescribed threshold, and selecting the candidate having an auditory response to said electrical signal and tinnitus perception below the prescribed threshold upon application of said electrical signal.
To further achieve at least the above objects in a whole or in parts, there is provided a method of testing whether a patient""s tinnitus can be at least partially reduced, including applying an electrical signal capable of generating pseudospontaneous activity in an auditory nerve of at least one human to the patient""s auditory nerve, determining the patient""s response to said electrical signal, and adjusting, if the patient""s tinnitus is not at least partially reduced, a level of said electrical signal and repeating said determining step.
To further achieve at least the above objects in a whole or in parts, there is provided an apparatus of diagnosing whether a human is a candidate for tinnitus reduction using a neural prosthetic, including applying means for applying an electrical signal capable of generating pseudospontaneous activity in an auditory nerve of at least one human to a plurality of candidates, identifying means for identifying a prescribed threshold, and selecting means for selecting the candidate having an auditory response to said electrical signal and tinnitus perception below the prescribed threshold upon application of said electrical signal.
To further achieve at least the above objects in a whole or in parts, there is provided a method of determining residual effects to a patient with tinnitus resulting from application of a signal capable of inducing pseudo-spontaneous activity, including applying an electrical signal capable of generating pseudo-spontaneous activity in an auditory nerve of at least one human to the patient""s auditory nerve for a first time period, and determining whether there remains a perceptible difference in the patient""s tinnitus after said first time period.
To further achieve at least the above objects in a whole or in parts, there is provided a method for applying a high frequency signal to a nerve, including identifying a voltage level of high frequency signal that is sufficient to cause desired activity in the nerve, wherein the high frequency signal applied at said voltage level further is perceived as pain, modifying the high frequency signal to be the sufficient voltage level while the electrical signal remains substantially physiologically imperceptible to the patient, and applying the electrical signal to the auditory nerve to generate pseudospontaneous activity in the auditory nerve.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.